This invention relates to hyperthermia treatment of tissue by irradiation with microwave energy and, more particularly, to an novel microwave applicator having a variable radiation pattern.
Hyperthermia has received a great deal of attention in recent years as a form of cancer therapy. In hyperthermia, the temperature of a tumor is typically raised to the range of 42.degree. C. to 45.degree. C. Such temperatures can kill both malignant and normal cells. Hyperthermia is made practical by selective heating of tumors, either alone or in conjunction with chemotherapy or radiation therapy. Microwave energy has been used to provide hyperthermia treatment. The microwave energy is applied to malignant tissue by an applicator, which acts as an antenna, and is coverted to heat in the tissue. Both external, or surface, applicators and implantable applicators have been used. However, surface applicators are preferable from a convenience standpoint.
Significant problems have been encountered in selectively heating malignant tumors to the required temperature without overheating the surrounding normal tissue. Individual rectangular and circular waveguide sections having radiating apertures have been utilized for microwave hyperthermia treatment. See, for example, A. Y. Cheung et al, "Direct Contact Applicators for Microwave Hyperthermia," J. Microwave Power, 16(2), 1981, p. 151 and G. Kantor, "Evaluation and Survey of Microwave and Radiofrequency Applicators, " J. Microwave Power, 16(2), 1981, p. 135. However, individual microwave applicators are not effective in treatment of deep-seated tumors. Frequencies above about 500 MHz are rapidly attenuated in tissue and do not produce substantial heating at depths beyond about 1 or 2 cm. Lower frequencies experience less attenuation in tissue but cannot be focused with practical sized applicators.
This problem has been alleviated to some extent by the use of multiple applicators directed at a tumor from different directions resulting in an increased power level in the region where the radiation patterns intersect. The incident radiation can be incoherent or can be phase controlled to provide a phased array antenna. P. F. Turner in "Deep Heating of Cylindrical or Elliptical Tissue Masses," Third International Symposium: Cancer Therapy by Hyperthermia, Drugs, and Radiation, Fort Collins, Col. June 22-26, 1980, describes an annular phased array for hyperthermia treatment. The radiating apertures have fixed positions around a central opening in which the patient is located. Such applicator systems are large and expensive and require precise positioning of the patient. Furthermore, since the system is spaced apart from the patient, higher power levels are required to achieve the same amount of heating, and the danger associated with leakage of microwave power is increased.
Malignant tumors can be located virtually anywhere in the human body, ranging from the skin surface to deep-seated organs. Furthermore, the tumors can have virtually any size and shape. It is desirable to provide a microwave hyperthermia applicator which can effectively treat tumors regardless of their size, shape or location. Heretofore, microwave applicators have had a fixed configuration and, therefore, have lacked this flexibility.
It is a general object of the present invention to provide a novel microwave hyperthermia applicator.
It is another object of the present invention to provide a microwave hyperthermia applicator with a variable radiation pattern.
It is yet another object of the present invention to provide a microwave hyperthermia applicator capable of treating a variety of tumor locations, sizes and shapes.